The invention relates to an air conditioner for a motor vehicle having an arrangement for detecting refrigerant leaks and taking remedial measures in response thereto.
Unpublished German patent application to DE 44 26 339 A1, discloses an arrangement which deals with a safety aspect of air conditioners that use a refrigerant that is environmentally acceptable but flammable (for example, a hydrocarbon). When such a refrigerant is used, vehicle occupants may be endangered in the event of a leak in the refrigerant circuit, because a flammable mixture of air and refrigerant forms in the passenger compartment that can be ignited by a spark. In this patent application, it was proposed to eliminate this danger by continuously monitoring the air blown through the evaporator for any hydrocarbons in the air stream, using a suitable gas sensor, shutting off the refrigerant circuit if required.
The object of the present invention is to provide an improved arrangement for protecting against refrigerant leaks in a vehicle air conditioner, such that in the event of a leak in the refrigerant circuit the vehicle occupants will not be endangered and will be warned in time, with monitoring being effective even when the air conditioner is not switched on and/or an air stream is not conducted into the passenger compartment.
This object is achieved according to the invention, which can detect a leak in the refrigerant circuit, independently of whether the air conditioner is switched on or off, by monitoring the pressure in the refrigerant circuit. If the pressure drops below a minimum value, the air conditioner is shut off and/or the air stream from the fresh-air intake is cut off if necessary. In addition to use by itself, this safety device can of course also be used in combination with the gas sensor according to the older patent application and the advantageous embodiments mentioned therein, thus increasing redundancy and safety.
In one advantageous embodiment of the invention the pressure sensor is provided with a time-differentiating measurement curve so that it responds only to rapid pressure changes, and not to slow ones. In other words, this embodiment responds only to pressure changes that exceed a presettable time pressure gradient. As a result, slow pressure changes related to operation are disregarded, as are minor leaks that pose no risk to the occupants. Unnecessary or avoidable response of the warning device can thus be avoided.
In addition, it can be advantageous for the blower that delivers fresh air to be automatically adjustable for maximum delivery in the event the pressure sensor responds. This results in maximum dilution with air of the vapors formed or escaping, and brings the resultant vapor/air mixture below a concentration that can be ignited.
Another advantageous embodiment includes a control device which has the vapor pressure curve of the refrigerant stored therein, and the evaporator is provided with a temperature sensor. The presettable response threshold of the pressure sensor can thus be adjusted automatically and continuously by the control device as a function of the evaporator temperature in such fashion that the pressure at the pressure sensor that corresponds to the response threshold is always below the respective working point of the vapor pressure curve of the air conditioner. As a result, a false alarm caused by a decrease in refrigerant pressure during normal operation can be avoided. (The refrigerant pressure normally drops at lower outside temperatures.)
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.